Under normal conditions, the bacteria are placed on the mucosa of the intestinal epithelium and does not penetrate into the body. However, contrary to what most people think, the gut microflora has an influence that extends beyond the intestinal lumen.
The intestinal microflora acts on three levels:
• Level 1: Bacteria – bacteria interaction
• Level 2: Bacteria – intestinal mucosa interaction
• Level 3: Bacteria – host immune system interaction.
At the first level, bacteria interact with other bacteria, either beneficial as pathogenic. At this level, the beneficial bacteria and commensal establish symbiotic relationships with other, but also release important substances such as lactic acid and bacteriocins that allow them to control and compete with the pathogenic flora.
At the second level, the microflora initiates the interaction with the host throughout the intestinal microvilli. In this sense, bacteria establish recognition between the lipopolysaccharides present in the bacterial wall with the receptors present in the membrane of the enterocytes. This recognition is very important because it allows the creation of beneficial interactions with immune intestinal cells and allows the maintenance of mucosa integrity.
At the third level, bacteria contact with the host immune system, thanks to the presence of the dendritic cells located in the basal part of the intestinal mucosa. Dendritic cells are the most powerful antigen presenting cells and control the type of immune response to be established (pro-inflammatory or regulatory), as well as its location after making antigen presentation.
Dendritic cells are, therefore, very efficient in controlling the delicate balance between tolerance and immunity in an environment exposed to a huge quantity of antigens as intestines are. Any factor affecting dendritic cells activity can have an impact on its functionality, even in the development of intestinal pathologies like celiac disease or inflammatory bowel disease.